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What is the effect of ethanol concentration on bread flavor?

Therefore, does changing the yeast's ethanol production affect the bacteria which produce lactic and acetic acid, whereby influencing bread flavor?

lerner
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  • The source I cite in [this answer](https://cooking.stackexchange.com/a/112740/20413) suggests that some breads can contain alcohol in measurable quantities – Chris H May 24 '21 at 08:15
  • @lerner you are conflating yeast and bacteria. Sourdough is risen by gasses given off by lactic acid producing bacteria, whereas conventional doughs are risen by yeasts. Yeasts have different flavours to bacteria. You may or may not have both yeast and bacteria in a sourdough starter and any given loaf. – bob1 May 24 '21 at 09:14
  • @bob1: I'm not sure there is a misunderstanding here. The aerobic bacteria in the starter could be affected in an interesting way by an increase in ethanol concentration. But how can one vary the yeast to increase ethanol concentration? – Mark Wildon May 24 '21 at 10:22
  • @MarkWildon What I'm saying is that generally in yeast risen dough bacteria don't play a role in the flavour much, if at all, because they largely aren't present at high enough numbers or the right types. Conversely in bacterial risen ones, yeast aren't present and ethanol isn't produced (much), by the [lactic acid fermentation pathway](https://www.khanacademy.org/science/ap-biology/cellular-energetics/cellular-respiration-ap/a/fermentation-and-anaerobic-respiration) (see pathway diagram about 1/3 way down page). – bob1 May 24 '21 at 10:38
  • Thanks for the responses all. @bob1 I'm pretty sure that yeasts are what rise all breads? The link you provide shows that the lactic acid fermentation pathway doesn't give off CO2, whereas the alcohol fermentation path undergone by yeast does. I did some more research and came across [this](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3147428/) which, as is logical, suggests that bacteria don't like alcohol. Perhaps maximizing the amount of aerobic respiration (decreasing ethanol) maximizes bacteria growth, and hence the typical sourdough flavors. – lerner May 24 '21 at 23:02
  • @lerner Well, turns out I learned something new... yeasts are in most sourdoughs and do make up most of the levening effect. However some species of bacteria do contribute to this through the heterometabolic pathway, which outputs acetic, lactic acids + CO2. Bacteria are generally killed by EtOH; the same effect is why some people think weakly alcoholic beer etc was drunk before advent of clean water supplies. Looks like combo of yeast + bacteria is best, followed by yeast alone then bacteria alone for rising power. I'll try to add refs later. – bob1 May 25 '21 at 02:03
  • I see. Glad to learn more about the bacterial contributions myself :) – lerner May 25 '21 at 08:21

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